1. Field of the Invention
The present invention relates to an insert-molding method for obtaining resin-molded products in which insert products such as electronic parts are sealed with a resin to a sufficient degree without deviation in position, and to a molding device therefor.
2. Description of the Related Art
In order to maintain the water-proof properties of electronic parts, there have heretofore been employed a method by which the surfaces of the electronic parts are covered with a potting material, a method by which a resin sealing plug is attached thereto, and the like method.
In recent years, however, there has been widely employed a method by which the surfaces are sealed with a resin in order to decrease the cost of products and to enhance the ratio of recycling. The sealing with the resin is generally based on an insert-molding method which features excellent mass-productivity at a decreased cost.
As the device used for the insert molding, there has heretofore been known the one disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 55-91642. That is, as shown in FIG. 10, there has been proposed a molding device 9 comprising a mold 90 having a cavity 91 in which will be arranged an insert product 2, and a holding pin 92 retractably provided in the mold 90 to hold the insert product 2 at a tip 921. Reference numeral 95 denotes a port for pouring-in the synthetic resin.
Described below is an insert-molding method using the above-mentioned mold 9.
First, the insert product 2 is arranged at a predetermined position in the cavity 91 being held by the holding pin 92. Next, the cavity 91 is filled with a synthetic resin 3 and, then, the holding pin 92 is retracted from the cavity 91. Thereafter, the cavity is further filled with the synthetic resin 3.
Thus, there is obtained a resin-molded product in which the whole surface of the insertion product is sealed with the resin.
According to the above-mentioned insert-molding method and device, however, the quality of the molded product is affected by the timing of retracting the holding pin 92 from the cavity 91. That is, when the holding pin 92 is retracted before the cavity 91 is completely filled with the synthetic resin 3, there remains no melted portion caused by the holding pin 92, and the sealing with resin is accomplished to a sufficient degree. Due to the synthetic resin 3 that is filled, however, the insert product 2 moves and its position is deviated. When the holding pin 92 is retracted after the cavity 91 is completely filled with the synthetic resin 3, on the other hand, the space in which the holding pin 92 used to be positioned is not sufficiently filled with the synthetic resin 3, and the insert product 2 is not sealed with the resin to a sufficient degree.
There has further been proposed a method according to which the synthetic resin 3 is forcibly extruded and introduced into space where the holding pin used to be positioned as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-163528 or Japanese Unexamined Patent Publication (Kokai) No. 8-306718.
That is, as shown in FIG. 11, a device 8 used for this method includes a mold 80 having a cavity 81, a cylindrical holding pin 82 retractably provided in the mold 80, and a pole-like moving pin 83 retractably provided in the holding pin 82.
Briefly described below is the insert-molding method by using the above-mentioned molding device 8.
That is, referring to FIG. 11, an insert product 20 is arranged in the cavity 81 and is held by the holding pin 82. The cavity 81 is then filled with the synthetic resin 3.
Then, as shown in FIG. 12, the moving pin 83 is moved in the direction of the cavity 81 while the holding pin 82 is retracted, and the synthetic resin 3 is forcibly extruded and introduced into space where the holding pin 82 used to be positioned.
The insert product 20 has a through hole 201 formed in the central portion thereof and an accessory 202 such as a reed frame on the end surfaces thereof, the accessory 202 extending beyond the cavity 81 so as to be held by the mold 80.
However, the above-mentioned conventional insert-molding method and device have problems as described below.
That is, after the synthetic resin 3 is introduced, the surface of the synthetic resin 3 contacting to the holding pin 82 is cooled by the holding pin 82, resulting in the formation of a skin layer (solidified layer on the surface of the resin) 31.
The holding pin 82 has a cylindrical shape and, hence, the skin layer 31 assumes a cylindrical shape, too, as shown in FIG. 13.
Therefore, the area of the skin layer 31 inevitably increases but is never concentrated to one point despite being extruded by the moving pin 83.
Accordingly, the skin layer 31 does not melt again despite of the ambient heat or pressure, and the unmelted portion is very likely to remain.
When the holding pin 82 is retracted at a delayed timing, therefore, the unmelted portion remains and the insert product 20 is not sealed with the resin to a sufficient degree.
The present invention was accomplished in view of the above-mentioned problem inherent in the prior art, and its object is to provide an insert-molding method capable of sealing an insert product with a resin to a sufficient degree without permitting the position of the insert product to be deviated as a result of suppressing the residence of the unmelted portion caused by the holding pin, and a molding device therefor.
A first aspect of the present invention is concerned with an insert-molding method in which an insert product is arranged in a cavity of a mold and is held by a holding pin, a molten synthetic resin is poured into said cavity, and said holding pin is retracted to obtain an insert-molding product in which said insert product is covered with said synthetic resin, wherein a moving pin is provided adjacent to said holding pin, said moving pin is moved in the direction of the cavity while retracting said holding pin after said cavity is filled with said synthetic resin, and said synthetic resin is extruded and introduced into space where said holding pin used to be positioned.
In the present invention, what most draws attention is that the moving pin is moved in the direction of the cavity while retracting the holding pin after the cavity is filled with the synthetic resin, and the synthetic resin is extruded and introduced into space where the holding pin used to be positioned.
A second aspect of the present invention is concerned with a molding device for carrying out the above-mentioned molding method to produce an insert-molding product in which an insert product is covered with a synthetic resin, comprising a mold having a cavity for molding, and a holding pin retractably provided in said mold to hold the insert product, wherein said mold has a moving pin that retractably moves in the direction of the cavity adjacent to said holding pin.
In this molding device, what most draws attention is that the moving pin retractably moves in the direction of the cavity adjacent to the holding pin.
Therefore, the molding device of the invention makes it possible to produce an insert-molding product in which the insert product is sealed with the resin to a sufficient degree while suppressing the deviation in position of the insert product.